Process for obtaining copper linings



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No Drawing. @riginai application June 7, 1937,

Serial No. 1%,9'34. Divided and this applicatlon October 12, 1939, Serial No. 299,208. In

Etaly Indy 1!, 1936 zCiaims. (cl. e1--ee.1)

The present application is a division of my earlier and copending application- Serial No. 146,974, filed June 7th, 1937.

The subject matter of my present invention is a process for w copper linings, e. g. for

the manufacture oi copper mirrors or copperplated silver mirrors, and the'copper or silver mirrors obtained by such method.

My present invention is based on the discovery that formaldehyde is capable, in the cold, of reducing the cuproglyceric (or cuprotartaric) complex to metallic copper in the presence of traces of precipitated silver, or traces of colloidal silver.

15 The invention is' now described in greater detail by means of the following exemplary embodiment thereof which, however, is solely illustrative and not limitative in character.

Exm

ride and distilled water. A known silvering solution. is prepared, comprising for instance ammoniacal silver nitrate and inverted sugar, and

- this solution is added in such manner that the silver is deposited in so thin a layer as to givethe glass a very faintly blue color if observed by transparency. The glass plate thus prepared is again washed with water, and then the solution (see below) is rapidly poured thereon so as to suddenly flood the whole plate.

Solution 40 added thereto.

According to my present invention the reaction between formaldehyde and caustic soda is prevented by the presence of traces of a colloid,

A sheet of glass is washed with stannous chlo-p such as gum arable, agar-agar or the like, as such reaction wouldproduce a consequent development of hydrogen which would cause the detachment of the copper layer from its support.

In order to obtain copper mirrors by starting from the glycerine (cuproglyceric) complex, it is necessary to operate with dilute solutions such as those above indicated, and adding formaldehyde thereto immediately before the use of the said solutions.

When operating at ordinary temperature for obtaining a good and sufficiently thick deposit of copper, a period of time of from one-half to one hour will be needed according to the temperature of the surrounding atmosphere.

A preferred form of the invention has been described above, but it will be understood by those skilled in the art, that both the solution and the process may be modified in their non-essential details without departing from the scope of my invention.

Having now particularly described and ascertained the nature of my said invention and in what manner'thesarne is to be performed, what is claimed is:

l. The process for the production of copper linings 'for the manufacture of copper mirrors, coppered silvered mirrors and the like, comprising precipitating metallic copper in the cold by reduction with a reducing agent consisting of formaldehyde invthe presence of silver from a solution consisting of caustic soda, gum arabic, a cuproglycerate, and water.

2. The process for the production of a copper lining upon a support, comprising first producing a very thin layer of silver on said support, and then precipitating a lining of metallic copper in the cold on said thin silver layer by reduction with a reducing agent consistingof formaldehyde from a solution consisting of caustic soda, gum arabic, a cuproglycerate, and water.

-. PAOLO MSCIA'I'I'EIJI. 

